Microwave mode changer and integrator



Aug. 29,1950 v E. G. UNDER 2,520,504

MICROWAVE MODE CHANGER vAND INTEGRATOR Filed April 30, 1947 Brwentor atentecl ug.

MICROWAVE MODE CHANGERAND.

INTEGRATOR Ernest `G. Linder, Princeton, NLJ., assignor to Radio Corporation of America, a-corporation of Delaware measuring frequency sufiiciently high that numerous higher order microwave modes arelencountered. Such standing wave distribution within the shielding enclosure heretofore has necessitated the utilizationV of a large number of microwave detectors'spaced at various points within the shielding enclosure, and integrating means for deriving an yaverageindication of the microwave energy detectedl at the numerous spaced points. Frequently, it is impracticable to'space numerous microwave detectors at a sufficiently large number of points within the media under observation or to move a single microwave detector to a- V.plurality'of vpoints within said enclosure.

The instant invention contemplates an irnproved method of and means for effectively changing the microwave vmodes within av relatively large shielding' enclosure at a relatively rapid rate rso that a single microwave detector having a relatively long time constant effectively integrates the microwave energy distribution throughout the shielding enclosure. A first yembodiment of the invention utilizes a reciprocating piston or similar device for varyingv one of the internal dimensions of the microwave enclosure at a suiiiciently high rate to provide-'effective integrationof the microwave energy withinf the enclosure by a microwave detector and'indicator having ya relatively long time constant.

A second embodimentI of the invention utilizes a plurality of rotating vanes or propeller blades which are rotated within the microwavel enclosure by means of a shaft or magnetic coupling coupled to a driving motor located outside of the microwave enclosure. By proper shaping of the rotating vanes and control of their rotating speed, a much more ecctive integration of the microwave energy may be provided than is possible with a reciprocating piston device. A modication of saidfiirst embodiment of the invention having a reciprocating element within the micro- Wave enclosure utilizes -a hollow pyramidal shielding element having sides parallell to and adjacent to the sides of the microwave enclosure adjacent to one of the corners thereof wherein the hollow pyramidal-element isl reciprocated on an axis extendingisubstantially from opposite corners of the yhollow rectangular microwave enclosure. Thus Yeach of the dimensions of the microwave enclosure may be'varied simultaneously.

A third embodiment of the invention eectively provides rapid variation of the'microwave moding in va-microwave enclosure by energizing the media withinthe enclosure by frequency-modulated microwave energy, the modulating frequency being higher than the modulation response frequency ofthe microwave detector coupled into' theenclosure.

Among the objects or" the invention are to provide improved methods of and means for measuring microwavev energy. Another object is to provide improved methods of and means-for electively integrating microwave energy having a plurality of higher order modes within a microwave enclosure. An additional object of the invention is to provide improved methods of and means for eiectively integrating microwave energy within a shielding enclosure having a plurality of microwave modes wherein the modes are varied at a higher rate than the response rate of a microwave detector coupled into said enclosure. A still further object of the invention is to' provide improved methods of and means for effectively integrating `microwave energy in a shielding enclosure by rapidly mechanically varying vat least one internal dimension of said enclosure at a rate higher than the response frequency of `a microwave detector and indicator coupled within-saidenclosure. Another object of the invention is to' provide an improved method of and means'for eiectively integrating microwave energy within a shielding enclosure by introducir-ig,A frequency-mo,d-ulatedv energy into said enclosure, the modulation frequency being higher than the responseA frequency of a microwave detector andindicator coupled into said enclosure. Still another object of` the invention is to provide improved methods of and means for efiectively integrating the absorption of microwave energy in a microwave absorptive medium within a microwave shielding enclosure.

The invention will be described in greater de.- tail by reference to the accompanying drawing of which Figure vl is a cross-sectional, elevational View rvof a rstembodiment of thev invention employing a movable piston device,.Figure 2 is a cross-sectional planview of a second embodiment mechanism, not shown. It should be .understood that the internal dimension of the resonator may be varied in any other known manner, such as by ergy transfer of the resonator and will be substantially independent of microwave moding therein.

Figure 3 illustrates schematically a method and apparatus for accomplishing integration of microwave energy transfer through a cavity resonator enclosing a gas or other material to be analyzed, wherein the material-irradiating microwave energy source comprises a frequency-modulated microwaVe-generator 'I coupled through the input transmission line 9 and the input coupling loop I I into the cavity resonator I. The modulation frequency of the frequency-modulated microwaves should be suiciently high to provide effec- Y, tive integration of the irradiating microwave ena movable or deformable wall section either con-4' tiguous with the remaining resonator structure,

or connected thereto by a Sylphon bellows. The travel of the reciprocating system is indicated by the dimension A source 1 of microwave energy is coupled into the cavity resonator I through a transmission line 9 and a coupling loop II.V A medium, such as a microwave absorptive gas or other material, may be introduced into the lcavity resonator I for observation of its microwave absorptioncharacteristics. The cavity resonatorV I must, of necessity, be large with respect to the operating wavelength for many microwave absorption measurements in order to provide the required sensitivity. The reciprocating action of the piston '3 varies the microwave modes in the resonator I at a relatively high frequency so that the electric field at all points, except at the Vresonator inner walls, passes through all walues from Zero to maximum several times during each cycle of the piston, and the resonator .consequently shifts through numerous electrical modes.

A microwave detector andindicator I3 coupled into the cavity resonator` through an output loop or other pickup device I5 has a time constant which is long with respect to the electrical mode changing period. Thus vmicrowave energymdetected and indicated will effectively be integrated to-provide indications of the averagedenergy transferv of the resonator, and the higher order modes of theresonatorare eiectively eliminated insofar as l*the indications arerconcerned.V

Figure 2 illustrates a second mechanical embodiment of the invention wherein the mircowave resonator I includes a rotary device I1 having a plurality of rotatable conductive vanes I9, each of which has a dimension which is at least one wavelength at the'operating frequency. The rotating structure Il is supported on a center bearing ZI and, if desired, may be driven directly by coupling its center shaft to an external motor. As illustrated, the rotary structure I1 includes magnetic iron pole pieces 23 which are driven by an external permanent magnet device 25 rotated by a Vmotor 21. The resulting induction drive by the magnet 25 of the pole pieces 23 and Y vane supporting structure I1 is eective through the copper or brass external shell 29 of the cavity resonator I. The vanes I9 may be shaped in any desired manner to .provide maximum variation of the microwave modes within the resonator I. The speed of rotation of the rotary vanes I9 should be sufficiently high to vary the electric eld at'all points Within the resonator through all `values from zero to maximum at a rate higher than the time constant of the microwave detector and indicator circuit. Thus the indicator V will provide indications of the average microwave,en-,-A

t, ergy for a microwave detector and indicator of any selected time constant. By utilizing an indicator of the cathode ray tube having a sweep or timing frequency synchronized with the modulating frequency, a complete spectrum of the microwave modes may be observed. Then by substituting an indicatorl having a'relatively long time constant, the modes maybe effectively integrated and the average energy transfer of the cavity resonator may be indicated.

Figure 4 illustrates a modification of the embodiments of the invention illustrated in Figs. 1 and 2 wherein a hollow pyramidal conductive element 29 enclosed within the cavity resonator I is caused to move along an axis extending from opposite corners 3I, 33 of the resonator by means of av reciprocating shaft coupled to a reciproeating mechanism,- not shown. The shaft 35 eX- tends through any suitable bearing in the corner 3| ofthe cavity resonator, and reciprocating motion thereof causes all three ofthe inner dimensions of the resonator to be varied simultaneously thereby` providing maximum variation of the microwave modes within the resonator. The frequency of the reciprocating motion of the pyramidal conductive element 29 must be suiciently high to provide effective integration of the microwave energy transfer to the resonator for a microwave detector and indicator of predetermined time constant. It should be understood that the hollow pyramidal reciprocating element 29 may be varied'in shape as desired to provide the desired variation of microwave moding and to minimize resonance effects of the reciprocating ele- IIlGIlt.' j Y Y ThusY the invention described and claimed herein includes novel methods of and means for varying the electrical characteristics of a microwave resonator for effectively providing integration of microwave energy transferred therethrough, wherein the moding variation period is short as compared to the time constant ofthe microwave detector and indicating circuits. In each of the electromechanical embodiments of the invention described heretofore, the movable mechanical element for disturbing the microwave energy moding may be of conductive or dielectric material and preferably should be at least as large as one wavelength at the operating microwave frequency.

I claim as my invention:

l. In combination, a cavity resonator including a movable element enclosed therein, the proportions of said element and its rate and path period of variation of microwave moding in said resonator to provide output signal energy characteristic of the integrated value of signal energy of a. plurality of modes in said resonator.

2. In combination, a cavity resonator including a movable element enclosed therein, the proportions of said element and its rate and path of motion providing variation of microwave moding in said resonator with substantially no variation in the tuning of said resonator, means for coupling microwave signal energy into said resonator, means for varying continuously the position of said element within said resonator, and a wave detector coupled into said resonator, said detector having a time constant substantially greater than the period of variation of microwave moding in said resonator to provide detected signal energy characteristic of the integrated value of signal energy of a plrality of modes in said resonator.

3. Apparatus according to claim 1 wherein said resonator is rectangular and wherein said movable element conforms to a corner of said resonator.

4. In combination, a rectangular cavity resonator having internal dimensions exceeding a wavelength at the operating frequency including a movable coductive element conforming to a corner of said resonator and having dimensions exceeding one-half Wavelength at said operating frequency enclosed therein, the proportions of said element and its rate and path of motion providing variation of microwave moding in said resonator with substantially no variation in the tuning of said resoator, means for varying continuously diagonally the position of said element within said resonator, and an output circuit coupled into said resonator, said circuit having a time constant substantially greater than the period of variation of microwave moding in said resonator to provide output signal energy characteristic of the integrated value of signal energy of a plurality of modes in said resonator.

5. In combination, a rectangular cavity resonator having internal dimensions exceeding a Wavelength at the operating frequency including a movable conductive element forming a corner of said resonator and having dimensions exceeding one-half wavelength at said operating frequency enclosed therein, the proportions of said element and its rate and path of motion providing variation of microwave moding in said resonator with substantially no variation in the tuning of said resonator, means for coupling micro- Wave signal energy into said resonator, means for varying continuously diagonally the position of said element within said resonator, and a wave detector coupled into said resonator, said detector having a time constant substantially greater than the period of variation of microwave moding in said resonator to provide detected signal energy characteristic of the integrated value of signal energy of a plurality of modes in said resonator.

6. In combination, a cavity resonator having internal dimensions exceeding a wavelength at the operating microwave frequency, a movable element having a plurality of rotatable vanes each exceeding one-half wavelength at said operating frequency and entirely disposed within said resonator, means disposed externally of said resonator for rapidly rotating 'said element to vary rapidly the moding of microwaves in said resonator, and an output circuit coupled into said resonator, said circuit having a time constant substantially greater than the rate of variation of microwave moding in said resonator to provide output signals characteristic of the integrated value of signals of substantially all modes in said resonator.

ERNEST G. LINDER.

REFERENCES CITED The following references are of record in the l file of this patent:

UNITED STATES PATENTS Number Name Date 2,157,855 Koch May 9, 1939 2,306,282 .Samuel Dec. 22, 1942 2,405,277 Thompson Dec. 2, 1943 2,413,939 Benware Jan. 7, 1947 2,426,177 `Carlson Aug. 26, 1947 2,466,439 Kannenberg Apr. 5, 1949 

